Abstract: To address the problem of cyclic-loading-caused damage of surrounding rocks in underground engineering,graded cyclic loading tests were conducted to study the nonlinear dynamic characteristics and inelastic deformation properties of red sandstone under different confining pressures.The results indicate that with the increase of confining pressure,the peak deviatoric stress of red sandstone increases,and the failure mode transits from tensile-splitting to shear failure.The deformation of rock specimens involves three stages:crack closure,stable crack growth,and unstable crack propagation.Both the closure stress and dilatancy stress increase with confining pressure,yet the ratios of closure stress and dilatancy stress remain stable.As the confining pressure increases,the dynamic modulus and damping ratio increase,but the dynamic Poisson’s ratio decreases.Under cyclic loading,as the deviatoric stress level increases,the dynamic modulus initially increases and then decreases,while the damping ratio and dynamic Poisson’s ratio exhibit a fluctuating increase and an continuous increase,respectively.In the meantime,the residual strain and fatigue strain proportion of the rock specimens increase.With the increase in confining pressure,the total energy,elastic strain energy,and dissipated energy of the specimens all show a gradual upward trend.Based on statistical damage mechanics and Weibull distribution,as well as using the Drucker-Prager yield criterion as the failure criterion,a nonlinear damage constitutive model is proposed,and the theoretical prediction of stress-strain relationship agrees well with experimental data.